buflib: Remove CRC checks

The CRC is a fairly useless safety check because we already
have specific checks to validate the metadata, and CRCs are
only verified before calling the move callback. Removing the
check should not significantly reduce buflib's robustness.

Change-Id: Ica99bd92fc514819b4fd9f359b4272e581020f75

2 files changed, 4 insertions, 96 deletions

diff --git a/firmware/buflib.c b/firmware/buflib.c
index 457a47b109..f71d992153 100644
--- a/firmware/buflib.c
+++ b/firmware/buflib.c
@@ -33,7 +33,6 @@
 #include "string-extra.h" /* strmemccpy() */
 #include "debug.h"
 #include "panic.h"
-#include "crc32.h"
 #include "system.h" /* for ALIGN_*() */
 
 /* The main goal of this design is fast fetching of the pointer for a handle.
@@ -101,17 +100,11 @@
 #define PARANOIA_CHECK_LENGTH       (1 << 0)
 #define PARANOIA_CHECK_HANDLE       (1 << 1)
 #define PARANOIA_CHECK_BLOCK_HANDLE (1 << 2)
-#define PARANOIA_CHECK_CRC          (1 << 3)
-#define PARANOIA_CHECK_PINNING      (1 << 4)
+#define PARANOIA_CHECK_PINNING      (1 << 3)
 /* Bitmask of enabled paranoia checks */
 #define BUFLIB_PARANOIA \
     (PARANOIA_CHECK_LENGTH | PARANOIA_CHECK_HANDLE | \
-     PARANOIA_CHECK_BLOCK_HANDLE | PARANOIA_CHECK_CRC | \
-     PARANOIA_CHECK_PINNING)
-
-#if BUFLIB_PARANOIA & PARANOIA_CHECK_CRC
-# define BUFLIB_HAS_CRC
-#endif
+     PARANOIA_CHECK_BLOCK_HANDLE | PARANOIA_CHECK_PINNING)
 
 /* Forward indices, used to index a block start pointer as block[fidx_XXX] */
 enum {
@@ -124,18 +117,11 @@ enum {
 enum {
     bidx_USER,      /* dummy to get below fields to be 1-based */
     bidx_PIN,       /* pin count */
-#ifdef BUFLIB_HAS_CRC
-    bidx_CRC,       /* CRC, protects all metadata behind it */
-#endif
 };
 
 /* Number of fields in the block header. Note that bidx_USER is not an
  * actual field so it is not included in the count. */
-#ifdef BUFLIB_HAS_CRC
-# define BUFLIB_NUM_FIELDS 5
-#else
-# define BUFLIB_NUM_FIELDS 4
-#endif
+#define BUFLIB_NUM_FIELDS 4
 
 struct buflib_callbacks buflib_ops_locked = {
     .move_callback = NULL,
@@ -179,16 +165,6 @@ static void check_handle(struct buflib_context *ctx,
 static void check_block_handle(struct buflib_context *ctx,
                                union buflib_data *block);
 
-/* Update the block's CRC checksum if CRCs are enabled. */
-static void update_block_crc(struct buflib_context *ctx,
-                             union buflib_data *block,
-                             union buflib_data *block_end);
-
-/* Check the block's CRC if CRCs are enabled. */
-static void check_block_crc(struct buflib_context *ctx,
-                            union buflib_data *block,
-                            union buflib_data *block_end);
-
 /* Initialize buffer manager */
 void
 buflib_init(struct buflib_context *ctx, void *buf, size_t size)
@@ -387,7 +363,6 @@ move_block(struct buflib_context* ctx, union buflib_data* block, int shift)
     check_block_handle(ctx, block);
     union buflib_data *h_entry = block[fidx_HANDLE].handle;
     union buflib_data *block_end = h_entry_to_block_end(ctx, h_entry);
-    check_block_crc(ctx, block, block_end);
 
     if (!IS_MOVABLE(block) || block_end[-bidx_PIN].pincount > 0)
         return false;
@@ -741,7 +716,6 @@ buffer_alloc:
 
     union buflib_data *block_end = block + BUFLIB_NUM_FIELDS;
     block_end[-bidx_PIN].pincount = 0;
-    update_block_crc(ctx, block, block_end);
 
     handle->alloc = (char*)&block_end[-bidx_USER];
 
@@ -1011,11 +985,6 @@ buflib_shrink(struct buflib_context* ctx, int handle, void* new_start, size_t ne
         block = new_block;
     }
 
-    /* update crc of the metadata */
-    union buflib_data *new_h_entry = new_block[fidx_HANDLE].handle;
-    union buflib_data *new_block_end = h_entry_to_block_end(ctx, new_h_entry);
-    update_block_crc(ctx, new_block, new_block_end);
-
     /* Now deal with size changes that create free blocks after the allocation */
     if (old_next_block != new_next_block)
     {
@@ -1089,9 +1058,6 @@ void buflib_check_valid(struct buflib_context *ctx)
             continue;
 
         check_block_handle(ctx, block);
-        union buflib_data *h_entry = block[fidx_HANDLE].handle;
-        union buflib_data *block_end = h_entry_to_block_end(ctx, h_entry);
-        check_block_crc(ctx, block, block_end);
     }
 }
 #endif
@@ -1202,60 +1168,3 @@ static void check_block_handle(struct buflib_context *ctx,
         }
     }
 }
-
-#ifdef BUFLIB_HAS_CRC
-static uint32_t calc_block_crc(union buflib_data *block,
-                               union buflib_data *block_end)
-{
-    union buflib_data *crc_slot = &block_end[-bidx_CRC];
-    const size_t size = (crc_slot - block) * sizeof(*block);
-    return crc_32(block, size, 0xffffffff);
-}
-
-static void update_block_crc(struct buflib_context *ctx,
-                             union buflib_data *block,
-                             union buflib_data *block_end)
-{
-    (void)ctx;
-
-    if (BUFLIB_PARANOIA & PARANOIA_CHECK_CRC)
-    {
-        block_end[-bidx_CRC].crc = calc_block_crc(block, block_end);
-    }
-}
-
-static void check_block_crc(struct buflib_context *ctx,
-                            union buflib_data *block,
-                            union buflib_data *block_end)
-{
-    if (BUFLIB_PARANOIA & PARANOIA_CHECK_CRC)
-    {
-        uint32_t crc = calc_block_crc(block, block_end);
-        if (block_end[-bidx_CRC].crc != crc)
-        {
-            buflib_panic(ctx, "buflib crc mismatch [%p]=%08lx, got %08lx",
-                         &block_end[-bidx_CRC],
-                         (unsigned long)block_end[-bidx_CRC].crc,
-                         (unsigned long)crc);
-        }
-    }
-}
-#else
-static void update_block_crc(struct buflib_context *ctx,
-                             union buflib_data *block,
-                             union buflib_data *block_end)
-{
-    (void)ctx;
-    (void)block;
-    (void)block_end;
-}
-
-static void check_block_crc(struct buflib_context *ctx,
-                            union buflib_data *block,
-                            union buflib_data *block_end)
-{
-    (void)ctx;
-    (void)block;
-    (void)block_end;
-}
-#endif
diff --git a/firmware/include/buflib.h b/firmware/include/buflib.h
index e54ec72a99..349e4a3e7a 100644
--- a/firmware/include/buflib.h
+++ b/firmware/include/buflib.h
@@ -43,7 +43,6 @@ union buflib_data
     char* alloc;                  /* start of allocated memory area */
     union buflib_data *handle;    /* pointer to entry in the handle table.
                                      Used during compaction for fast lookup */
-    uint32_t crc;                 /* checksum of this data to detect corruption */
 };
 
 struct buflib_context
@@ -64,7 +63,7 @@ struct buflib_context
  * The total number of bytes consumed by an allocation is
  * BUFLIB_ALLOC_OVERHEAD + requested bytes + pad to pointer size
  */
-#define BUFLIB_ALLOC_OVERHEAD (5*sizeof(union buflib_data))
+#define BUFLIB_ALLOC_OVERHEAD (4*sizeof(union buflib_data))
 
 /**
  * Callbacks used by the buflib to inform allocation that compaction